1. Field of the Invention
The present invention relates to a sheet feeding apparatus that supplies a sheet from a sheet holding portion into a feed path, and particularly to a sheet feeding apparatus in which a feeder roller disposed in a feed path and a pickup roller disposed in a sheet holding portion are driven by a single driving source.
2. Description of Related Art
For instance, there is known a sheet feeding apparatus disposed in an inkjet printer and feeding a sheet from a sheet supply tray to a sheet catch tray along a feed path. The inkjet printer includes a recording head and records an image on the sheet supplied from the sheet supply tray by ejecting ink droplets from the recording head onto the sheet. The sheet is supplied from the sheet supply tray into the feed path and then fed along the feed path, by operation of two rollers that may be respectively called pickup roller and feeder roller. To the two rollers, a driving torque or a rotary motion of a motor as a driving source is transmitted. To transmit the driving torque from the motor to each of the two rollers, a transmission mechanism constituted by a combination of a gear, a timing belt, and/or others is employed.
The pickup roller operates to supply the sheet, that is, to feed out the sheet from the sheet supply tray into the feed path. The feeder roller operates to feed the sheet along the feed path. The required properties are different between the pickup roller and the feeder roller. For instance, a required precision in a speed at which the sheet is supplied or fed, and whether a deskew capability is required or not, are different between the pickup roller and the feeder roller. Hence, the pickup roller and the feeder roller are controlled to rotate differently from each other. There is known an arrangement for giving a driving force to each of the two rollers which are controlled to differently rotate, where a driving source is provided for each of the two rollers. There is also known an arrangement for a printer where a driving torque is transmitted from a single driving source to a plurality of driven portions, as disclosed in JP-A-3-272880. Further, JP-A-61-149379 and JP-A-60-145873 disclose an arrangement for rotating one of two rollers depending on a direction in which a driving source is rotated, by use of a one-way clutch or a planetary gear.
With respect to an image recording apparatus such as an inkjet printer, there is a demand for downsizing of the apparatus and speed-up of image recording. To meet the demand for downsizing, the sheet supply tray is downsized or reduced in thickness. Further, a guide is disposed on the sheet supply tray such that the position of the guide is variable on the sheet supply tray so that sheets in a variety of sizes, e.g., sheets in A4, B5 and legal sizes and postcard, can be selectively placed or set on the sheet supply tray. On the other hand, sometimes it is desired to include in an image recording apparatus another sheet supply tray on which a large stack of sheets of a kind that is frequently used, such as of A4 size, can be set. This sheet supply tray for holding a large stack of sheets will be hereinafter referred to as “sheet supply cassette”.
To meet the demand for the speed-up of image recording, there has been proposed an image recording apparatus in which the mode of sheet feeding is selectable, that is, one of a normal feeding mode and a high-speed feeding mode is selected. When the normal feeding mode is selected, image recording is performed to sheets that are one by one supplied into the feed path at a normal speed. When the high-speed feeding mode is selected, on the other hand, image recording is performed to sheets that are supplied into the feed path with a distance between each two sheets consecutively fed being reduced.
The image recording apparatus including the sheet supply cassette on which a large stack of sheets can be set necessarily further includes a transmission mechanism for transmitting a driving torque from a motor as a driving source to another pickup roller corresponding to the sheet supply cassette. On the other hand, the image recording apparatus capable of making a selection between the normal feeding mode and the high-speed feeding mode includes two transmission mechanisms for transmitting driving torques of two motors, respectively, namely, a first transmission mechanism for transmitting to the pickup roller a driving torque of a first motor that is for the normal feeding mode, and a second transmission mechanism for transmitting to the same pickup roller a driving torque of a second motor that is for the high-speed feeding mode.
It is often the case that an image recording apparatus of high-end model is equipped with the sheet supply cassette and the high-speed feeding mode as standard settings, but an image recording apparatus of popular model or entry model is not. Further, depending on preference of a user and irrespective of whether the model is high-end or entry, sometimes an image recording apparatus is equipped with further another sheet supply tray and/or is constructed such that a still higher-speed feeding mode is optionally settable. It is undesirable to enable these various settings by designing for each of the settings a transmission mechanism and a drive switching mechanism, and preparing components, such as a gear and a shaft, exclusively for each model, since it costs high. That is, to reduce the cost of an image recording apparatus, it is desirable to use as many components as possible commonly among various models.
In the image recording apparatus which can be optionally equipped with a sheet supply tray or cassette, and/or in which the high-speed or higher-speed feeding mode is settable, it is desired to transmit a driving torque from a motor to a pickup roller and a feeder roller by means of a simple arrangement, while reducing the cost of the components of the image recording apparatus as well as enhancing the efficiency of assembling of the image recording apparatus.